Daily intake of lactating crossbred cows grazing elephant grass rotationally
(1)Luiz Januário Magalhães Aroeira(2), Fernando César Ferraz Lopes(2), João Paulo Guimarães Soares(3), Fermino Deresz(2), Rui da Silva Verneque(2), Pedro Braga Arcuri(2) e Leovegildo Lopes de Matos(2)
Abstract The goal of this trial was to estimate the total dry matter (TDMI) and daily pasture dry matter intakes (PDMI) by lactating crossbred Holstein Zebu cows grazing elephant grass (Pennisetum purpureum Schum.) paddocks submitted to different rest periods. Three groups of 24 cows were used during two years. The paddocks were grazed during three days at the stocking rate of 4.5 cows/ha. Treatments consisted of resting periods of 30 days without concentrate and resting periods of 30, 37.5 and 45 days with 2 kg/cow/day of 20.6% crude protein concentrate. From July to October, pasture was supplemented with chopped sugarcane plus 1% urea. Total daily dry matter intake was estimated using the extrusa in vitro dry matter digestibility and the fecal output with chromium oxide. Regardless of the treatment the estimated average TDMI was 2.7, 2.9 and 2.9±0.03% and the mean PDMI was 1.9, 2.1 and 2.1±0.03% of body weight in the first, second and third grazing day, respectively (P<0.05). Only during the summer pasture quality was the same whichever the grazing day. Sugarcane effectively replaced grazing pasture, mainly in the first day when pasture dry matter intake was lowest.
Index terms: Pennisetum purpureum, digestibility, extrusion, dry matter content, feed grasses.
Consumo diário de vacas mestiças em lactação em pastejo rotacionado de capim-elefante
Resumo O objetivo deste trabalho foi o de estimar o consumo total e o diário de matéria seca do pasto, de vacas mestiças Holandês Zebu, em piquetes de capim-elefante (Pennisetum purpureum
Schum.). Três grupos de 24 vacas foram usados em piquetes (4,5 vacas/ha), pastejados por três dias e submetidos a diferentes períodos de descanso durante dois anos. Os tratamentos consistiram de des-cansos de 30 dias sem concentrado e 30, 37,5 e 45 dias com a suplementação de 2 kg de concentrado (20,6% de proteína bruta). De julho a outubro, as vacas receberam, como suplementação, cana-de-açúcar mais 1% de uréia. O consumo total de matéria seca foi estimado a partir da digestibilidade
in vitro da matéria seca da extrusa e da produção fecal obtida com óxido crômico. Independentemente do tratamento, o consumo total foi 2,7; 2,9 e 2.9±0,03%, e o consumo de matéria seca do pasto foi de 1,9; 2,1 e 2,1±0,03% do peso vivo (p<0,05), respectivamente, no primeiro, segundo e terceiro dia de ocupação do piquete. Somente no verão, o consumo do pasto foi semelhante nos três dias de pastejo. A mistura cana-de-açúcar e uréia substituiu o pasto, principalmente no primeiro dia de pastejo, ocasião em que o consumo do pasto era mais baixo.
Termos para indexação: Pennisetum purpureum,digestibilidade, extrusão, conteúdo da matéria seca, gramíneas forrageiras.
Introduction
Pennisetum purpureum
Schum. known as
El-ephant grass or Napier grass is a tall erect perennial
tropical grass, with thick stems up to 4.5 m high,
found on moist soils in areas with over 1,000 mm of
annual rainfall. Elephant grass grows best on deep
soils of moderate to fairly heavy texture and
toler-ates short droughts, but does not withstand
water-logging. It yields very large quantities of dry matter,
(1)Accepted for publication on May 4, 2001.
(2)Embrapa-Centro Nacional de Pesquisa de Gado de Leite,
Rua Eugênio do Nascimento, 610, CEP 36038-330 Juiz de Fora, MG. E-mail: laroeira@cnpgl.embrapa.br, ferraze@dedalus.lcc.ufmg.br, deresz@cnpgl.embrapa.br, rsverneq@cnpgl.embrapa.br, pba1@cnpgl.embrapa.br, leomatos@cnpgl.embrapa.br
(3)Universidade Estadual Paulista, Faculdade de Ciências Agrárias
but is low in protein content unless cut very young.
It should not be cut closer than 10-15 cm from the
ground. Under normal management, stands are
in-vaded by weeds and run out after two or three years
so that they have to be ploughed up and replanted
(Tropical Feeds, 1999).
Although traditionally used as chopped grass in
Brazil, there is evidence of the great potential of
el-ephant grass as pasture. Results of milk production
with crossbred cows grazing elephant grass, at
Embrapa-Centro Nacional de Pesquisa de Gado de
Leite, in Brazil, between 10,000 and 15,000 kg/ha,
during the 180 days of rainy season, were reported
by Deresz (1994) and Coser et al. (1996). However,
elephant grass shows a high stocking rate only
dur-ing the rainy season, since forage production is
dras-tically reduced in the dry months. In South-eastern
Brazil, elephant grass dry matter availability
de-creases from over 3,500 kg/ha in November, to less
than 500 kg/ha in July (Aroeira et al., 1999). One of
the alternatives to minimize this problem is the
supplementation with chopped sugarcane.
Sugarcane is readily available as forage for dairy
cattle and is used as a strategic supplementation
par-ticularly during the dry season. Both the sugar and
fiber contents of sugarcane are high, but protein and
lipid contents are very low (Valadares Filho et al.,
1990; Aroeira et al., 1993). Milk productions over
15,000 kg/ha/year were reached with cows grazing
elephant grass supplemented with sugarcane plus urea
mixture during the dry season (Deresz &
Mozzer, 1990).
The objective of this trial was to estimate the daily
composition of extrusa, dry matter and elephant grass
dry matter intakes of lactating crossbred Holstein
Zebu cows grazing paddocks submitted to different
resting intervals.
Material and Methods
The trial was carried out from April 1992 to October 1993 at Embrapa-Centro Nacional de Pesquisa de Gado de Leite, in Minas Gerais State, Brazil, at approximately 22o latitude South and 43o longitude West, at an average
altitude of 426 m. In this region there are two well-de-fined seasons. The dry season lasting from April/May to September/October characterized by average temperatures of 17ºC and scarce rainfall (60 mm per month). The rainy
season lasts from October to March, with average tem-perature of 24ºC and monthly rainfall of about 230 mm.
As in all South hemisphere, in Brazil the autumn months are March, April and May, the winter months are June, July and August, the spring months are September, October and November and the summer months are De-cember, January and February.
An area of 5.3 ha planted with elephant grass (Pennisetum purpureum Schum.) was used. The pasture was fertilized with 200 kg of N, 200 kg of K2O, 40 kg of
P2O5 and 1,000 kg of dolomite limestone per ha/year.
Ni-trogen and K fertilizers were applied in November, Janu-ary and March. The limestone and phosphorous were hand distributed in November.
Three groups of 24 crossbred Holstein Zebu cows each were used. These had an average of 45 to 60 days in milk, in their second or third lactation, and averaged 483±5.3 kg of live weight. The first group of cows calved in February or March and entered the experimental area in April and remained until October (1992). The second group calved in August or September and stayed in the experimental area from October to April 1993. The third group calved in February or March and remained in the experimental area from April to October (1993). These animals were blocked taking into account the milk yield and live weight data from the pre-experimental period. A total of six cows per treatment (three per replication) were kept at all times. The cows were milked twice a day, at 7 a.m. and 2 p.m. and had free access to a mineral mix-ture and water before milking.
The area planted with elephant grass was divided into paddocks, alternately grazed for three consecutive days, and allowed different resting periods, making up the four experimental treatments, replicated twice, as follows: rest-ing period of 30 days without concentrate supplementa-tion (30W) and resting periods of 30 (30C), 37.5 (37.5C) and 45 (45C) days with concentrate supplementation. The number of paddocks and their areas varied according to the treatment in such a way that stocking rate was always about 4.5 cows/ha. Thus, for a resting period of 30 days, there were 11 paddocks of 607 m2 each. For a resting
pe-riod of 37.5 days, 13 paddocks of 494 m2 and one
pad-dock of 247 m2 (grazedfor one day and half) and for the
45 day resting periods, 16 paddocks measuring 417 m2
each.
From October to June elephant grass was the only roughage available to the cows. During the driest months (July to October) the animals grazed elephant grass dur-ing the night and were confined between milkdur-ing, in sepa-rate corrals, according to treatment, where they received chopped sugarcane plus 1% urea (9 parts of urea and 1 part of ammonium-sulfate) ad libtum.
The daily intake measurements were taken 16 times during the entire experimental period. Intake was estimated in April, May (autumn), July, August (winter) September, November (spring) and December (summer) of 1992 and January, February (summer), March, April, May (autumn), July, August (winter), September, October (spring) of 1993. Two esophageal fistulated dry cows, adapted to the graz-ing conditions, without fastgraz-ing, were used to estimate qual-ity of the forage intake. Material collection (extrusa) was carried out on three consecutive days, while the experi-mental cows grazed the same paddock. The fistulated cows were maintained in extra paddocks, for at least two weeks before the first collection period, managed at the same way of the experimental area, to be adapted to the forage. The two cows were moved from paddock to paddock after the amount of forage sampled was achieved (1.5 kg/cow). The samples were collected in the morning, between 9 and 12 a.m., weighed and oven-dried at 65oC for 72 hours,
before being analyzed for in vitro dry matter digestibility (IVDMD), following the method proposed by Tilley & Terry (1963).
The DM was determined at 100oC and the CP by the
Kjeldahl method (Association , 1990). The NDF and ADF were analyzed following the recommendations of Soest et al. (1991).
Fecal production was estimated using chromic-oxide (Cr2O3) as an external marker, at a rate of 10 g/animal/
day, administered orally, wrapped in paper, with aid of a speculum, during 12 days, in two doses of 5 g each, im-mediately before milking times. Feces were collected fresh twice a day directly from the concrete floor or by rectal grabbing, from the 6th to 12th day while chromium was
administered. Daily samples from the fecal collection pe-riod were pooled for analysis on an individual animal ba-sis. Each sample was dried at 65oC, ground through 1 mm
sieves and submitted to digestion by nitro-chloric acid, following the methodology proposed by Kimura & Miller (1952). After chemical digestion, chromium (Cr) was de-termined by atomic absorption spectrophotometry. Fecal production (FP) was then calculated using the formula: FP = Cr administered (g/day)/Cr in the fecal DM (g/kg).
Daily DM intake (DMI) was estimated using the for-mula:
DMI (g/day) = FP/(1-(digestibility/100)).
In the treatment where the diet was exclusively elephant grass, the formula above was applied directly. However, when the animals received the concentrate supplementa-tion or when sugarcane plus urea was administered, the intake of this supplements was daily measured and the IVDMD of each feed was determined. The fecal output was separated by feed components and their fecal contri-bution was subtracted from the total fecal output. Elephant grass or herbage DMI was obtained by difference. Daily DMI was estimated with the extrusa IVDMD sampled at the first, second and third day of the occupation period and the fecal production was obtained 24 hours after that. The experiment was conducted in a split-split plot de-sign. Cows and treatments were arranged as main plots. Years were arranged as subplots and the seasons as split-sub-plots. The statistical analysis was carried out using the General Linear Model Procedures (GLM) of Statisti-cal Analyses System (SAS Institute, 1993).
Results and Discussion
In both years elephant grass dry matter
availabil-ity was different (P<0.05), according to the season
(Table 1). The DM availabilities increased from
win-ter to summer in both years. However, as the dry
sea-son (winter and spring) was more severe in 1993,
daily herbage allowance in that period was lower
(P<0.05) than in 1992.
Means DM availabilities of 2,423, 1,939 and
1,745±92 kg/ha of DM were observed for resting
periods of 45, 37.5 and 30 days, respectively.
No difference was detected (P>0.05) in average daily
herbage allowances for the various resting periods,
due to the different sizes and number of paddocks.
The mean herbage allowance observed during the
experimental period was 11.3±0.45 kg/cow/day of
DM (Aroeira et al., 1999).
Similar elephant grass DM availability have
al-ready been described in Southeastern Brazil. In the
same experimental area Soares (1998) reported
2,354 kg/ha of DM in March. Benedetti & Colmanetti
(1997) recorded mean availability of 4,248 kg/ha of
DM during the rainy season. On the other hand, Olivo
et al. (1992) and Coser et al. (1996) observed annual
averages from 2,000 to 2,500 kg/ha of DM,
respec-tively.
by data obtained at the second (11.8%) and finally at
the third grazing day (10.5%).
Mean cell wall content as measured as NDF was
higher (P<0.05) in summer than all other seasons
al-though there was no difference in IVDMD among
them (Table 2). Elephant grass growth rates are higher
in wet summers with most of the dry matter being
cell wall (Passos, 1994). Other higher neutral
deter-gent fiber contents in elephant grass during the rainy
season were described in the literature (Anindo &
Potter, 1994; Soares, 1998).
In general, the mean IVDMD obtained at the first
day were similar among treatments (P>0.05), and
higher (P<0.05), than that observed at the second day,
except during the summer. The data recorded at the
third day were the lowest ones. Regardless of the
season of the year, average chemical composition of
extrusa varied (P<0.05) according to the grazing day,
as shown in Tables 2 and 3. It is suggested that
warmer temperatures (Soest, 1994) associated with
selective grazing, resulted in increased levels of NDF
and ADF, simultaneously as CP and IVDMD
de-creased.
Selective grass dry matter intake was the main
factor since the changes were observed from the first
through the third grazing days. During summer time
extrusa IVDMD was similar during the second in
relation to the first grazing day, probably because of
more abundant rainfall. Nonetheless, other factors
may have contributed to the chemical composition
of elephant grass such as the amounts of rainfall and
fertilizer applied, as well as soil composition and
sampling methodology. Soares (1998) reported for
the same area CP of 14.1 and 16.5, 14.1 and 19.1,
12.1 and 13.5 and 15.2 and 15.3% from an extrusa
sample collected, respectively, during winter, spring,
summer and autumn, from pastures fertilized with
300 and 700 kg/ha/year of nitrogen. In the present
trial, extrusa composition varied also according to
the grazing day and the experimental year, the
IVDMD recorded in 1992 (59.5, 59.2 and 55.5%)
were higher (P<0.05) than that observed in 1993
(53.7, 52.2 and 50.6%).
The data reported for extrusa composition were
in general higher in quality than that described for
samples of chopped elephant grass, as described by
(1)Values with different letters differ significantly within line (upper case) or within column (lower case) at 5% of probability by Tukey test.
Autumn Winter Spring Summer
Grazing day
DMD NDF DMD NDF DMD NDF DMD NDF
--- (%)
---1 59.6Aa 69.3Bc 58.1Aa 69.8Bc 48.7Bc 70.0Bc 60.0Aa 72.3Ab
2 55.9Bb 71.2Bb 54.9BCb 71.0Bb 53.9Ca 73.2Ab 58.1Aa 72.5Ab
3 53.8Abc 72.5Ba 52.3Bc 72.1Ba 50.8Bb 74.5Aa 55.3Ab 74.0Aa
Standard error 0.53 0.21 0.59 0.23 0.61 0.24 0.83 0.33
Table 2. In vitro dry matter digestibility (DMD), and neutral detergent fiber (NDF), as percentage of dry matter, from extrusa, according to the grazing day and season(1).
(1)Values with different letters differ significantly within line (upper case) or within column (lower case) at 5% of probability by Tukey test.
Season 1992 1993
DM/ha DM/cow/day DM/ha DM/cow/day
---(kg)---Autumn 1,864Bb 10.8Bb 2,582Aa 14.9Aa
Winter 1,332Ac 7.6Ac 547Bb 3.2Bc
Spring 2,161Aab 12.5Aab 1,680Bb 9.7Bb
Summer 2,633Aa 15.1Aa 2,950Aa 17.0Aa
Standard error 130 0.66 130 0.66
Anindo & Potter (1994) and Lopes & Aroeira (1998),
probably due to the animals allowance to select their
diet from those samples.
Considering the experimental design used in this
work the extrusa composition results (Table 2)
showed differences regardless the resting periods.
Therefore, taking into account the number of
pad-docks, the 30 days resting periods are recommended.
In addition, paddocks grazed every 30 days showed
higher CP content and lower NDF level, with no
sig-nificant effect on dry matter intake or milk
produc-tion, when compared to paddocks grazed every 37.5
or 45 days (Aroeira et al., 1999).
For DM intake calculation, feces produced 24
hours after the extrusa sampling were always used.
For example, for the calculation related to the first
day DMI, data from extrusa collected at the first
graz-ing day in a paddock and fecal output of the third
day grazed at the previous paddock were used. For
the second day DMI, data used came from extrusa
collected at that same day as well as fecal output from
the first grazing day. The same procedure was adopted
for the third grazing day. Data related to the fecal
output collected 48 hours after the collected extrusa
were not tested.
The average total dry matter intake as percentage
of body weight (BW), independent of treatment,
sea-son or experimental year, differed (P<0.05) relatively
to grazing day. Values of 2.86, 3.02 and 3.10±0.33%
of the BW, respectively, were observed at the first,
second and third grazing days (Table 4).
Pasture dry matter intake did not differ among
treatments, except during the summer (Aroeira et al.,
1999). However, the daily intake was different
ac-cording to the season of the year. Pasture dry matter
intake (Table 4) was highest during summer, lowest
in winter and intermediate in autumn and spring. In
general, PDMI increased significantly from the first
to second and third grazing day, being the last two
values similar. In addition, spring PDMI values were
similar at the first and second days.
Total and pasture dry matter intake were higher
during the summer probably due to more pasture
availability and decreased during autumn due to the
reduction of elephantgrass DM availability (Table 4).
Total dry matter intake was higher again during
win-ter due to sugarcane plus urea supplementation and
remained high during spring when elephant grass
resumed its growth (Table 1).
Considering the dry matter intake in relation to
the three grazing days/paddock, the means TDMI and
PDMI increased from the first to the third grazing
day (P<0.05). These data differ from the literature.
Higher forage intake should be expected in the first
grazing day based on the pasture availability and
for-age quality (Table 2). However, the probable reasons
for the results obtained in this trial, could be due to
the following factors: a) higher forage NDF content
observed at the third grazing day (Table 3); b) lower
rumen passage rate due to inferior forage quality;
c) higher rumen fill in the third grazing day.
During both dry seasons sugarcane plus urea was
administered, as a roughage supplement to the cows
between milking, in separated corrals, according to
treatment. The sugarcane plus urea intake was
re-corded by weighing the offered and the refused feed
every seven consecutive days, in each treatment
group. Independently of treatment, the average
sug-(1)Values with different letters differ significantly within line (upper case) or within column (lower case) at 5% of probability by Tukey test.
30W 30C 37.5C 45C
Grazing day
DMD NDF DMD NDF DMD NDF DMD NDF
--- (%)
---1 58.9Aa 69.9Bb 53.7Bab 69.4Bc 57.0Aa 71.1Ac 56.8Aa 70.9Ac
2 54.1Bb 71.9Ba 55.3Ba 70.9Cb 57.7Aa 72.3ABb 55.6Bab 73.0Ab
3 52.3Bc 72.6Ba 53.3Ab 73.2Ba 52.1Bb 73.1Ba 54.5Ab 74.3Aa
Standard error 0.63 0.24 0.63 0.24 0.62 0.24 0.64 0.24
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arcane dry matter intake was higher in the first than
in the second and third grazing days, the latter two
were similar. DM data collected as mean of
treat-ment groups were 1.35, 1.29 and 1.29±0.01% BW
for the first, second and third days, respectively. The
highest (P<0.05) intake in the first day was possibly
caused by a substitution effect, since pasture dry
matter intake was lowest in the first day.
Cows body weight varied with the experimental
treatments (P<0.05). Supplemented cows from the
experimental treatments mean live body weight of
484±5.3 kg were heavier than unsupplemented cows
(472±5.3 kg).
Conclusions
1. Forage intake in the first day is lower than that
grazed in the third day.
2. Only in summer pasture quality is similar among
grazing days.
3. During the dry season, sugarcane effectively
replaces grazing pasture dry matter intake.
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Autumn Winter Spring Summer
Grazing day
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-- (%)
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